Method and apparatus for driving electro-luminescence display panel

ABSTRACT

A method and apparatus for driving an electro-luminescence display panel capable of preventing an initial blinking phenomenon occurring at a power application is disclosed. In the method, a first electrode of the EL cell and a ground voltage source are opened during a first period from a turn-on time of a power source to shut off a current path of the EL cells. Then, the first electrode of the pixel matrix and the ground voltage source is shorted during a second period to form a current path such that the EL cells are light-emitted in accordance with a data supplied to the pixel matrix.

This application claims the benefit of Korean Patent Application No.P2004-11588 filed in Korea on Feb. 20, 2004, which is herebyincorporated by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to an electro-luminescence display (ELD), andmore particularly to a method and apparatus for driving anelectro-luminescence display panel that is capable of preventing aninitial blinking phenomenon occurring at a power application.

2. Description of the Related Art

Recently, there have been highlighted various flat panel display devicesreduced in weight and bulk that is capable of eliminating disadvantagesof a cathode ray. tube (CRT). Such flat panel display devices include aliquid crystal display (LCD), a field emission display (FED), a plasmadisplay panel (PDP) and an electro-luminescence (EL) display panel, etc.

The EL display panel of these display devices is a self-luminous devicecapable of light-emitting a phosphorous material by a re-combination ofelectrons with holes. The EL display panel is largely classified into aninorganic EL device using an inorganic compound as the phosphorousmaterial and an organic EL device using an organic compound as it. Sincesuch an EL display panel has many advantages of a low-voltage driving, aself-luminescence, a thin film type, a wide viewing angle, a fastresponse speed, and a high contrast, etc., it has been expected as apost-generation display device.

Generally, the organic EL device is comprised of an electron injectionlayer, an electron carrier layer, a light-emitting layer, a hole carrierlayer and a hole injection layer that are sequentially disposed betweena cathode and an anode. In such an organic EL device, if a desiredvoltage is applied between the cathode and the anode, electronsgenerated from the cathode are moved, via the electron injection layerand the electron carrier layer, into the light-emitting layer whileholes generated from the anode are moved, via the hole injection layerand the hole carrier layer, into the light-emitting layer. Thus, thelight-emitting layer emits a light by a re-combination of electrons andholes fed from the electron carrier layer and the hole carrier layer,respectively.

As shown in FIG. 1, an active matrix type EL display panel employingsuch an organic EL device includes a pixel matrix 20 having sub-pixels28 arranged at each area defined by each intersection between gate linesGL and data lines DL, a gate driver 22 for driving the gate lines GL ofthe pixel matrix 20, a data driver 24 for driving the data lines DL ofthe pixel matrix 20, and a power supply 32 and a ground voltage sourceGND connected to the pixel matrix 20.

The gate driver 22 applies scanning pulses to sequentially drive thegate lines GL.

The data driver 24 supplies R, G and B data signals to each data line DLwhenever the scanning pulse is applied. At this time, the data driver 24converts digital data inputted from the exterior thereof into analogdata signals. For instance, the data driver 24 voltage-divides a gammareference voltage inputted from the exterior thereof into a plurality ofgamma voltage levels, and selects the gamma voltage level correspondingto the input digital data to apply it as an analog data signal.

One pixel is implemented by a combination of the R, G and B sub-pixels28. If the scanning pulse is applied to the gate line GL, then each ofthe R, G and B sub-pixels 28 receive a data signal from the data line DLto generate a light corresponding to the data signal. To this end, asshown in FIG. 2, each of the R, G and B sub-pixels 28 includes an ELcell OEL having a cathode connected to the ground voltage source GND,and a cell driver 30 connected to the gate line GL and the data line DLto control a current amount fed to an anode of the EL cell OEL from apower line PL, thereby driving the EL cell OEL.

The cell driver 30 includes a switching thin film transistor T1 having agate terminal connected to the gate line GL, a source terminal connectedto the data line DL and a drain terminal connected to a node N1, adriving thin film transistor T2 having a gate terminal connected to thenode N1, a source terminal connected to the power line PL and a drainterminal connected to the EL cell OEL, and a storage capacitor Cconnected between the power line PL and the node N1.

If the scanning pulse is applied to the gate line GL, then the switchingthin film transistor T1 is turned on to thereby apply a data signalsupplied to the data line DL, via the node N1, to the gate terminal ofthe driving thin film transistor T2. At this time, the storage capacitorC charges a difference voltage between a driving voltage VDD suppliedvia the power line PL and the data signal supplied to the node N1. Thedriving thin film transistor T2 controls a current amount I fed from thepower line PL to the EL cell OEL in response to a voltage supplied tothe node N1, thereby controlling a light-emitting amount of the EL cellOEL. Further, when the switching thin film transistor T1 is turned off,the driving thin film transistor T2 supplies a constant current I untila data signal at the next frame is applied by a voltage charged in thestorage capacitor C, thereby keeping a light-emission of the EL cellOEL.

In the conventional EL display panel having the above-mentionedconfiguration, as the power supply 32 is turned on, an initial drivingvoltage VDD is supplied to the pixel matrix 20 prior to an applicationof the data signal from the data driver 24. For this reason, since theEL cells OEL forms a current path by the initial driving voltage VDDsuddenly supplied to the pixel matrix 20, there is raised a problem inthat an initial blinking phenomenon occurs.

SUMMARY OF THE INVENTION

Accordingly, it is an object of the present invention to provide amethod and apparatus for driving an electro-luminescence display panelthat is capable of preventing an initial blinking phenomenon occurringat a power application.

In order to achieve these and other objects of the invention, a methodof driving an electro-luminescence display panel, having a plurality ofelectro-luminescence (EL) cells, according to one aspect of the presentinvention includes the steps of opening a first electrode of the EL celland a ground voltage source during a first period from a turn-on time ofa power source to shut off a current path of the EL cells; and shortingthe first electrode of the pixel matrix and the ground voltage sourceduring a second period to form a current path such that the EL cells arelight-emitted in accordance with a data supplied to the pixel matrix.

In the method, said first period includes a time interval from a turn-ontime of the power source until an ending time of at least first frame.

The method further includes the step of detecting said first period byutilizing a vertical synchronizing signal for dividing said data foreach frame.

A driving apparatus for an electro-luminescence display panel accordingto another aspect of the present invention includes a pixel matrixhaving a plurality of sub-pixel each including an EL cell and a celldriver for controlling a current supplied to the EL cell in accordancewith a data; a ground voltage source connected to a cathode of the ELcell; a power source connected to the power source line; and a groundvoltage source controller for opening the cathode and the ground voltagesource during a first period from a turn-on time of the power source toshut off a current path of the EL cells, and for shorting them during asecond period to light-emit the EL cells in accordance with a supplieddata.

In the driving apparatus, the ground voltage source controller detectssaid first period by utilizing a vertical synchronizing signal fordividing said data for each frame.

In the driving apparatus, the ground voltage source controller includesa switching device for switching a connection between the cathode of theEL cell and the ground voltage source; and a latch for controlling theswitching device using said vertical synchronizing signal.

Herein, the latch opens the switching device from a turn-on time of thepower source until an ending time of at least first frame and thereaftershorts the switching device.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other objects of the invention will be apparent from thefollowing detailed description of the embodiments of the presentinvention with reference to the accompanying drawings, in which:

FIG. 1 is a schematic block circuit diagram showing a configuration of aconventional organic electro-luminescence display panel;

FIG. 2 is an equivalent circuit diagram of the sub-pixels shown in FIG.1;

FIG. 3 is a block circuit diagram showing a configuration of a drivingapparatus for an organic electro-luminescence display panel according toan embodiment of the present invention; and

FIG. 4 is a waveform diagram of a vertical synchronizing signal appliedto a ground voltage source controller shown in FIG. 3.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

Reference will now be made in detail to the preferred embodiments of thepresent invention, examples of which are illustrated in the accompanyingdrawings.

Hereinafter, the preferred embodiments of the present invention will bedescribed in detail with reference to FIGS. 3 and 4.

FIG. 3 is a block circuit diagram showing a configuration of adriving-apparatus for an organic EL display panel according to anembodiment of the present invention.

Referring to FIG. 3, the driving apparatus for the EL display panelincludes a pixel matrix 40 having sub-pixels 54 arranged at each areadefined by each intersection between gate lines GL and data lines DL, agate driver 42 for driving the gate lines GL of the pixel matrix 40, adata driver 44 for driving the data lines DL of the pixel matrix 40, apower supply 46 and a ground voltage source GND connected to the pixelmatrix 40, and a ground voltage source controller 52 for controlling aconnection of the pixel matrix 40 with the ground voltage source GND.

The pixel matrix 40 includes R, G and B sub-pixels 54 provided for eacharea defined by each intersection between a plurality of gate lines GLand a plurality of data lines DL. Each pixel is implemented by acombination of the three R, G and B sub-pixels 54. If a scanning pulseis applied to the gate line GL, then each of the R, G and B sub-pixels58 receive a data signal from the data line DL to generate a lightcorresponding to the data signal. To this end, each of the R, G and Bsub-pixels 54 includes an EL cell OEL having a cathode connected to theground voltage source GND, and a cell driver 56 connected to the gateline GL and the data line DL to control a current amount fed to an anodeof the EL cell OEL from a power line PL, thereby driving the EL cellOEL.

More specifically, the cell driver 56 includes a switching thin filmtransistor T1 having a gate terminal connected to the gate line GL, asource terminal connected to the data line DL and a drain terminalconnected to a node N1, a driving thin film transistor T2 having a gateterminal connected to the node N1, a source terminal connected to thepower line PL and a drain terminal connected to the EL cell OEL, and astorage capacitor C connected between the power line PL and the node N1.

If the scanning pulse is applied to the gate line GL, then the switchingthin film transistor T1 is turned on to thereby apply a data signalsupplied to the data line DL, via the node N1, to the gate terminal ofthe driving thin film transistor T2. At this time, the storage capacitorC charges a difference voltage between a driving voltage VDD supplied,via the power line PL, from the power supply 46 and the data signalsupplied to the node N1. The driving thin film transistor T2 controls acurrent amount I fed from the power line PL to the EL cell OEL inresponse to a voltage supplied to the node N1, thereby controlling alight-emitting amount of the EL cell OEL. Further, when the switchingthin film transistor T1 is turned off, the driving thin film transistorT2 supplies a constant current I until a data signal at the next frameis applied by a voltage charged in the storage capacitor C, therebykeeping a light-emission of the EL cell OEL.

The gate driver 42 applies the scanning pulses to sequentially drive thegate lines GL.

The data driver 44 supplies R, G and B data signals RD, GD and BD toeach data line DL whenever the scanning pulse is applied. At this time,the data driver 44 converts digital data inputted from a timingcontroller (not shown) into analog data signals. For instance, the datadriver 44 voltage-divides a gamma reference voltage inputted from agamma reference voltage generator (not shown) into a plurality of gammavoltage levels, and selects the gamma voltage level corresponding to theinput digital data to apply it as an analog data signal.

The ground voltage source controller 52 opens the ground voltage sourceGND and the pixel matrix 40 until the power supply 46 is turned on andat least one frame of data is supplied, via the data driver 44, to thepixel matrix 40. Thus, a formation of a current path at the EL cell OELcaused by the initial driving voltage VDD prior to a writing of a datainto the pixel matrix 40 can be shut off to prevent an initial blinkingphenomenon.

More specifically, the ground voltage source controller 52 opens theground voltage source GND and the cathode CE of the pixel matrix 40until the power supply 46 is turned on and a data signal at the firstframe is written into the pixel matrix 40 by utilizing a verticalsynchronizing signal Vsync for dividing the data for each frame, andthereafter shorts the ground voltage source GND and the cathode CE ofthe pixel matrix 40, thereby forming a current path at the EL cell OELunder control of the cell driver 56.

To this end, the ground voltage source controller 52 includes aswitching device, that is, an NMOS thin film transistor NT connectedbetween the ground voltage source GND and the cathode CE of the pixelmatrix 40, and a latch, that is, a D flip-flop 50 for controlling theNMOS thin film transistor NT.

The D flip-flop 50 receives a driving voltage supplied by a turn-on ofthe power supply 46 as an input signal D, and receives a verticalsynchronizing signal Vsync as an enable signal GE in order to recognizethe first frame. The vertical synchronizing signal Vsync is applied, viathe data driver 44, from a timing controller (not shown) and then isinverted by an inverter INV to be thereby inputted as the enable signalGE. For instance, as shown in FIG. 4, the vertical synchronizing signalVsync toggled from a high logic into a low logic at a starting time ofeach frame F is inputted, via the inverter INV, as the enable signal GEof the D flip-flop 50. Thus, the D flip-flop 50 detects a time point Aat which the vertical synchronizing signal Vsync is toggled after thefirst frame was finished and outputs the driving voltage VCC supplied asthe input signal D as an output signal Q, thereby turning on the NMOSthin film transistor NT having kept a turn-off state to short the groundvoltage source GND and the cathode CE of the pixel matrix 40. Thus, thepixel matrix 40 can prevent a blinking phenomenon caused by a currentpath until the first frame was finished after the power source wasturned on. Further, the output signal Q of the D flip-flop 50 remains atthe driving voltage VCC supplied as the input signal D even though thevertical synchronizing signal Vsync is toggled for each frame with thelapse of time, so that the NMOS thin film transistor NT also keeps aturn-on state. Thus, the pixel matrix 40 is emitted in accordance with adata supplied via the data driver 44 to thereby display a picture.

As described above, according to the present invention, the groundvoltage source and the pixel matrix is opened until a power source isturned on and the first frame is finished to shut off a current path ofthe EL cell, thereby preventing an initial blinking phenomenon.

Although the present invention has been explained by the embodimentsshown in the drawings described above, it should be understood to theordinary skilled person in the art that the invention is not limited tothe embodiments, but rather that various changes or modificationsthereof are possible without departing from the spirit of the invention.Accordingly, the scope of the invention shall be determined only by theappended claims and their equivalents.

1. A method of driving an electro-luminescence display panel having a plurality of electro-luminescence (EL) cells, comprising the steps of: opening a first electrode of the EL cell and a ground voltage source during a first period from a turn-on time of a power source to shut off a current path of the EL cells; and shorting the first electrode of the pixel matrix and the ground voltage source during a second period to form a current path such that the EL cells are light-emitted in accordance with a data supplied to the pixel matrix.
 2. The method according to claim 1, wherein said first period includes a time interval from a turn-on time of the power source until an ending time of at least first frame.
 3. The method according to claim 1, further comprising the step of: detecting said first period by utilizing a vertical synchronizing signal for dividing said data for each frame.
 4. A driving apparatus for an electro-luminescence display panel, comprising: a pixel matrix having a plurality of sub-pixel each including an EL cell and a cell driver for controlling a current supplied to the EL cell in accordance with a data; a ground voltage source connected to a cathode of the EL cell; a power source connected to the power source line; and a ground voltage source controller for opening the cathode and the ground voltage source during a first period from a turn-on time of the power source to shut off a current path of the EL cells, and for shorting them during a second period to light-emit the EL cells in accordance with a supplied data.
 5. The driving apparatus according to claim 4, wherein the ground voltage source controller detects said first period by utilizing a vertical synchronizing signal for dividing said data for each frame.
 6. The driving apparatus according to claim 4, wherein the ground voltage source controller comprises: a switching device for switching a connection between the cathode of the EL cell and the ground voltage source; and a latch for controlling the switching device using said vertical synchronizing signal.
 7. The driving apparatus according to claim 6, wherein, the latch opens the switching device from a turn-on time of the power source until an ending time of at least first frame and thereafter shorts the switching device. 